Wound Healing Flashcards
Give a generalised overview of the process of wound healing.
slide 3
1. injury is caused by trauma
2. cell/matrix damage
3. inflammation
4. -repair - healing and fibrosis/scar
-regenration
- failure of healing
What is regeneration?
Replacement of lost or damaged tissue by a similar type derived from the proliferation of the surrounding undamaged cells
What is repair?
Replacement of lost or damaged tissue by granulation tissue which later matures into fibrous scar tissue.
what is healing?
The process of healing and repair is similar in many tissues
Healing is usually described with reference to a small skin wound.
What is healing by primary & secondary intention?
Healing by primary intention: the wound edges are in close apposition (so re-epithelialisation dominates healing)
Healing by secondary intention: the wound is more extensive and the wound edges are widely separated
(granulation tissue covers wound & wound area is reduced by contraction).
You then get re-epithelialisation from wound edges but also from residual appendages (hair follicles etc.)
What’s the first thing that happens when you injure yourself (within an hour)?
Haemostasis: involving the connective tissue and epithelium
-Platelet plug formation
-Fibrin clot formation
What are some examples of factors which inhibit the formation of the platelet plug and fibrin clot?
Aspirin - pain killer
Warfarin - treat blood clots
factor VIII deficiency (also inhibits wound healing)
What follows the process of haemostasis in wound healing (around 48 hours)?
involving the connective tissue and epithelium
Inflammation
Macrophage infiltration
Debridement
What happens exclusively in the connective tissue following haemostasis & debridement? (Granulation tissue formation 2 to 5 days)
involving the connective tissue
Granulation tissue formation:
-endothelial cell and fibroblast proliferation
-new blood vessels migrate from the wound edges
-small blood vessels are accompanied by fibroblasts and inflammatory cells
-collagen extra-cellular matrix
What is granulation tissue?
A loose cellular connective tissue with many plump, synthetic fibroblasts; dilated irregular blood vessels; and inflammatory cells
What happens in the connective tissue after granulation tissue formation (>5 days)?
involving the connective tissue
maturation occurs:
-Decreased cellularity
-Decreased vascularity
-Remodelling of collagen matrix
-Collagen cross linking
INVOLVES MMP’s1 and other proteases
What changes in the epithelium are happening alongside all these events in the connective tissue (1 to 3 days)?
Re-epithelialisation:
Proliferation of basal epithelial cells adjacent to the wound
Migration of basal epithelial cells across wound bed under fibrin scab to restore epithelial continuity
Epithelial cells differentiate and stratified squamous structures reform
slide 11 and muska images
Summarise the healing of a small skin wound.
1 hour - Haemostasis; platelet plug and clot formation
48 hours - Inflammation and debridement
2-5 days - Granulation tissue formation
>5 days - maturation, remodelling, wound contraction
1-3 days - re-epithelisation
look at slide 10
Is the control of wound healing a simple process?
No it’s a complex process involving convergence of signals from many sources.
slide 12
What dramatically impaired wound healing in guinea pigs?
Mononuclear (macrophage precursor) depletion
What are the traditional functions of macrophages?
-Phagocytosis
-Protease synthesis
-Regulation of immune cell function
What is the significance of macrophages in wound healing?
They produce growth factors like:
-FGF a/b, TGF-b, PDGF, VEGF
-other bioactive molecules:
1.Fibroblast recruitment and activity
-cell proliferation
-ECM synthesis
-protease (MMP) synthesis
- Endothelial cell recruitment and activity
What systemic factors could interfere with wound healing?
Age
Nutritional status (e.g vitamin deficiency, protein deficiency)
Iatrogenic (people on steroids)
Pre-existing medical conditions (e.g diabetes)
What local factors could affect wound healing?
Blood supply (poor blood supply can lead to infection)
Infection
Persistent irritation
Poor wound stability
Poor apposition of wound edges
Skin wounds: direction of incision- Langers lines
Ionising radiation
What are some possible complications of wound healing?
-Wound dehiscence (breakdown of wound)
-Contractures
-Keloid/hypertrophic scar formation
-Weak scars (incisional hernia)
-Pigmentation
-Neoplastic changes (Marjolin’s ulcer)
What is a keloid scarring?
A sharply elevated, progressively enlarging scar characterised by the formation of excessive amounts of collagen in the dermis during connective tissue repair.
It may spread beyond the margins of the original wound
Characteristically found in Afro-Carribean populations
Seen on the face but does not affect the oral mucosa
look at slide 16
what is a hypertrophic scarring?
Similar to keloid but does not spread beyond the wound margins
Will affect varied population groups
Seen on the face but does not affect the oral mucosa
look at slide 16
How do embryonic wounds heal?
Heal without scarring
How is scaring on the oral mucosa?
There is still scaring but it is less than the skin
